Method of coating paper



Dec. 9, 1924- J. TRAQUAIR METHOD OF COATING PAPER Filed Dec. 5 1 gb I ULNVENTOR. n?

ATTORNEYS.

Patented Dec. 9, 1924.

mural) sraras JOHN 'rRAoUAm, or ofiIIiLI-co'rma, onto, assrenon 'ro MEAD PULP AND PAPER com- PANY OEDAY roN, OHIO, A conronarron OF OHIO.

To reboot may concern: Y

":nrE'ri ron or oo'acr'me PAPER.

Applicationfiled December', 1920. Serial No. 427,934.

Be it known that I, JOHN TRAQUAIR, a

subject of the Kingof Great Britain, resid" ing at Chillicothe, 1n the county of Ross and State of Ohio, have invented-a new and useful Method of Coating. Paper,- ofwhichthc following is a.- specificatlon.

My invention relates totheart ot applying to paper a. coating of pigment. to fill .up

1 or level the'unevenness of thersurface and cover the fibers of the paper and providea good even'printing surface. F

In my. new method oflfcoatingxipaper I eliminate, among. others, twoof the :most olk jectionable features 'whicha are common too the methods now practiced; namely,;the use: ,of excessive 'quantitiesoflwater, and brush:

ing. My-method consists briefiy',=;in' apply: rdescriibed manner is easily rubbed off, and sit is necessary to. treat it witha. coating of size to fix and bind it to the paper.

ing to paper.v a concentrated.suspension, in water of finely .3 pulverized mlnerali vor plgment, commonly re'ferredto as .eolor,id 1y.-; ing the :paper 'and the n:ap lying a coatmg- 5,;

-' of size to bind the color tot epaper. When term color solution is commonly-used- For the purpose of illustration 1 have prepared a drawing in which,

Fig. 1 shows, diagrammatically, the principal elements of a machine for amylylng coating to one side of a roll of paper.

Fig. 2 shows apparatusfor coating paper on both sides simultaneously.

Fig.3 shows, diagrammatically, lhesuccessive stages of the process for coating and sizing pa Referring now to Fi '1, the paper to1be coated istaken from 't 1e roll 10 and after being coated and dried is rerolled at 11. The paper passes between rolls 12 and 13, the latter of which dips into the solution of color contained in a tub 14.. I have obical sense but in paper coatingpractice the tained the best results from a solution con-.

er on one side by my new method.

' 'in the :paper being exposed to the solution for amore or less definite length of time, according to the diameter of the rolls and the speed of the paper. During this time the paper absorbs-a substantial part of the water.--' Passing between the rolls the pig- -ment is. pressed down on the paper, filling the-inequalities and forming a fine smooth surface. A suflicient quantity of the water is absorbed by the paper before it passes from between the rolls that the coating is heretofore been an important part of all coating methods.

The coating applied in the above may bedone in a machine substantially like --that shown in Fig. 1, the tub 14 containing the words .solution or fcolor solution"? 3 are used they refer to the: suspension; of :Plg ment inrwater. 'oreother: vehicle; .That is, of course, not asolutionin the strictly chemsize-instead of color. .ButI prefer to pass it through the sizing machine immediately after-coating it, thus saving the time ofhandling it twice. This is shown in Fig. 3.

,where the paper is coated at A, dried by 1 passing through a drying device B, sized at, (l, and after being dried again at D is rvrolled at E. i

If desired the paper -1nay be passedthrough a second coating and sizing machine, and the otherside coated before it is rerolled. All of this will be understood by those skilled in the art and need not be described in greater detail here. In Fig. 2 I show a machine for coating both sides of the paper simultaneously. In this machine the 1'olls20 and 21 correspond to rolls 12 and 13, respectively, and roll 21 dips into a tub containing color for coatingfihe under side of the paper. For-coating the upper surface a roll 22 dips into color contained in a tub 23. The color that iscarried up by this roll is removed by a scraper 24 and fiowin down the scraper on to roll20 is deposite by the roll .on the. upper surface of the paper. After the paper is dried it may be run through a similar machine and both sides sized sinmltaneously.

' Following the custom in paper making machinery I prefer to make one of the rolls of the coating machine soft, preferably rubber covered, and the other hard. The paper This 1,518,371 PAT T orrrcs.

. rendered immobile; that is, set or fixed so it can no longer flow.

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may be passed through the machine at a high speed.

"lheoperation of my method is affected by two factors: the absorptivity of the paper 5 and viscosity of the color solution. Paper may be made more or less non-absorptive or water-resisting by the addition of suitable substances to the pulp. For this purpose What is known as rosin size is much used and I9, is put into the beater. According to the ;-quantity of rosin size used paper is known as hard sized or soft sized, the latter absorbing water more readily than the former. In the practice of my method I prefer a paper which would be classed as soft sized, using a solution of about two parts of pigment to one part of water. Because of the lar e quantity of water that must be "used in tne old methods of coating paper,

the water resisting quality of hard sized paper has been found advantageous. Soft sized paper becomes mushy -and its strength is much impaired by being made very wet. .-.\'ot only is less water used in coating paper by my method than by others, but as the coating and sizing are done in successive steps, the paper being dried between the steps, the paper is not wetted' enough to affeet its physical condition materially. In 0 other words, with the older methods a large quantity of water is used in a single step, where in my method a smaller quantity of water is used, and instead of being applied at one time it is used in two parts, that which is put on in the first stage of the operation being evaporated from the paper before the second part is put on. As before stated, the color solution has a consistency about that of cream; obviously, this contains too little water to make the paper soft or otherwise affect its condition materially during the normal operation of my process. The quantity of .water applied in the sizing operation is likewise too small to apprcciably affect the physical condition of the paper, it requiring only enough water to diffuse the colloidal binding material through the layer of pigment and bind it to the paper. Wetting paper expands it, that is, increases its sln'face area. One of the advantages of my method is that the expansion of the paper is so slight as to impose no limit on the width of paper which it is practicable to coat thereby.

The viscosity of the color solution may be varied to suit the requirements of the paper to be coated. If in. using a simple solution of pigment and water the absorbtion of water is found to be too rapid. it may be slowed down by the addition of a small quantity of a colloidal sizc.- For this purpose one or two per cent of size will usually be sutlicient and-in any case it will not exceed four or live per cent. The quantity of size used for this purpose is entirely too small to play any part in binding the coatting tot-he paper, so the second step in the method, that of sizing paper is carried out just the same, whether this small quantit of size is put. into the solution or not. I on thr other hand, the absorption is found to be too slow, it may be increased by adding small quantities of suitable chemicals; for example, about one-half per cent of sili cate of soda with straight clay color solution, or one per cent gum arabic with limecontaining color solutions, such as satin white. These products have the property of increasing the fluidity or lowering the viscosity of the color solution and thereby accelerating its penetrating quality.

It is seen from the foregoing, that the practice of my new method 'may begin in the manufacture of the paper to be coated, by making paper having the desired absorptivity. But when this is not done and paper of any given absorptivity is to be coated, the viscosity of the color solution may be varied to suit the paper, in the manner described. I have referred to rosin sized paper, but it is not to be understood that the applicability of my method is limited to rosin sized or any other particular kind of paper. The consistency of the rolor solution is made such as will enable a coating of desired weight to be deposited on the paper by the roller, and the absorptivity of the paper and viscosity of the solution are so coordinated or adjusted, one to the other, that the coating will be rendered immobile through absorption of its water by the paper, so that the smooth surface which is imparted to the coating by the rolls will be retained after the paper passes from between the rolls.

There are obvious advantages in reducing the quantity of water used in coating paper: Itgreatly reduces the cost of drying the paper, for the drying can be done with a fa r less extensive drying equpiment. It also eliminates the common paper coatingtroubles of grease spots, pin holes and bl'llsl. marks, and removes the limit on the width of paper that can be coated.

Because of the simplicity of the above described paper qoating process, paper may be coated by my method more economically than by any other method of which I am aware. Furthermore, the product is more uniform and combines the advantages of an uncoated paper with those of a coated-paper and is superior in quality for certain classes of printin Having fully described my new method of coating paper, and described suitable means for carrying out the method, what I claim as my invention. is as follows:

1. The method of coating paper which comprises applying to the paper a layer of color comprising a mixture of pigmental matter and water, the quantity of water beas a vehicle for the pigmental matter, and ubsequently applying a coating of size whereby to bind the color to the paper.

2. The method of coating paper which comprises applying a solution of color to the paper, drying the paper and then applying a size to bind the color to the paper.

3. The method of coating paper which comprises applying a solution of color to the paper, then subjecting the paper to pressure between rolls, drying the paper and then applyinga coating of size whereby to bind the color to the paper.

4. The method of coating paper that comprises passing the paper between rolls, one of which is immersed in a solution of color and whereby a layer of color is deposited on the paper, drying the paper and subse quently applying size to the coated surface, thereby fixing the coating to the paper.

5. The method of coating paper that comprises passing the paper between rolls, one of which is immersed in a solution containing approximately two parts of dry color to one part of water, both by weight; drying the paper and subsequently applying size to the coated surface whereby to bind the coating to the paper.

6. In the coating of paper in which the paper is given a coating of color and then a coating of size to bind the coating of color to the paper, the method which comprises applying a solution of color to the paper and then passing the paper between rolls, the penetrating quality of the solution being adjusted from time to time to the absorptivity of the paper, so that by the time the paper emerges from between the rolls the color will have become immobile from loss of its liquid.

7. In the coating of paper in which the paper is given a coating of color and then a coating of size to bind the coating of color to the paper, the method which comprises applying-a solution of color to the paper and then passing the paper between rolls, the penetrating quality of the-solution being adjusted to the absorptivityfof the paper, so that by the time the paper emerges from between the rolls the color will havev become immobile from loss of its liquid, drying the paper and then applying a size to bind the color to the paper.

8. In the coating of paperv in which the paper is given a coating of color and then a coating of size to bind the coating of color tothe paper, the method which comprises applying a solution of color to the paper and then passing the paper between rolls, the penetrating quality of the solution being adjusted to the absorptivity of the paper by increasing or decreasing the viscosity of the solution, so that by the time the paper emerges from between the rolls the color will have become immobile from loss of liquid.

9. The method of coating paper, that comprises applying a-color solution to the paper, said solution having a consistency about that of cream; drying the paper and then applying a solution of colloidal size, said solution containing no more water than is necessary to diffuse the colloidal substance throu hthe coating and bind it to the paper.

10. n the coating of paper in which the paper is given a coating ofcolor and then a coating of size to bind the coating of color to the paper, the method which comprises treating'the paper pulp with materials which will give to the paper a predetermined absorptivity; then after the paper is made, applying a solution of color and passing the paper between rolls, the solution being made to have viscosity appropriate to the absorptivity of the paper, so that by the time the paper emerges from between the rolls the color will have become immobile from loss of it liquid.

11. In the coating of paper in which the paper is given a coating of color and then a coating of size to bind the coating of color to the paper, the method, which comprises applying a layer of color comprising a mixture of pigmental. matter and water, the. quantity of water being limited to that which is required to act as a Vehicle for the pigmental matter, and then passing the paper between rolls, whereby the color is pressed down on the paper, filling the ingqualities, so as to form a'fine smooth surace. JOHN TRAQUAIR. 

